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Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Lecture 8 of 42
Monday, 11 September 2006
William H. Hsu Department of Computing and Information Sciences, KSU
KSOL course page: http://snipurl.com/va Course web site: http://www.kddresearch.org/Courses/Fall-2006/CIS Instructor home page: http://www.cis.ksu.edu/~bhsu
Reading for Next Class: Rest of Chapter 4, p. 151 onward, Silberschatz et al. , 5 th^ edition Sections 5.1 – 5.2, Silberschatz et al. , 5th^ edition JDBC Primer (to be posted on Handouts page)
Database Connectivity: ODBC & JDBC
Notes: PS1 Solutions, MP
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Basic Query Structure:
Review
z SQL is based on set and relational operations with certain modifications and enhancements z A typical SQL query has the form:
select A 1 , A 2 , ..., An from r 1 , r 2 , ..., r (^) m where P
Ai represents an attribute Ri represents a relation P is a predicate. z This query is equivalent to the relational algebra expression.
z The result of an SQL query is a relation.
∏ A 1 , A 2 ,Κ, An ( σ P ( r 1 × r 2 ×Κ× rm ))
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Update of a View:
Review
Update of a View:
Review
z Create a view of all loan data in the loan relation, hiding the amount attribute create view branch_loan as select branch_name, loan_number from loan z Add a new tuple to branch_loan insert into branch_loan values (‘Perryridge’, ‘L-307’) This insertion must be represented by the insertion of the tuple (‘L-307’, ‘Perryridge’, null ) into the loan relation
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Embedded SQL Embedded SQL
z The SQL standard defines embeddings of SQL in a variety of programming languages such as C, Java, and Cobol. z A language to which SQL queries are embedded is referred to as a host language , and the SQL structures permitted in the host language comprise embedded SQL. z The basic form of these languages follows that of the System R embedding of SQL into PL/I. z EXEC SQL statement is used to identify embedded SQL request to the preprocessor EXEC SQL END_EXEC Note: this varies by language (for example, the Java embedding uses
SQL { …. }; )
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
ODBCODBC
z Open DataBase Connectivity(ODBC) standard standard for application program to communicate with a database server. application program interface (API) to Ö open a connection with a database, Ö send queries and updates, Ö get back results. z Applications such as GUI, spreadsheets, etc. can use ODBC
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
ODBC (Cont.) ODBC (Cont.)
z Each database system supporting ODBC provides a "driver" library that must be linked with the client program. z When client program makes an ODBC API call, the code in the library communicates with the server to carry out the requested action, and fetch results. z ODBC program first allocates an SQL environment, then a database connection handle. z Opens database connection using SQLConnect(). Parameters for SQLConnect: connection handle, the server to which to connect the user identifier, password z Must also specify types of arguments: SQL_NTS denotes previous argument is a null-terminated string.
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
ODBC Code ODBC Code
z int ODBCexample() { RETCODE error; HENV env; / environment / HDBC conn; / database connection / SQLAllocEnv(&env); SQLAllocConnect(env, &conn); SQLConnect(conn, "aura.bell-labs.com", SQL_NTS, "avi", SQL_NTS, "avipasswd", SQL_NTS); { …. Do actual work … }
SQLDisconnect(conn); SQLFreeConnect(conn); SQLFreeEnv(env); }
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
ODBC Code (Cont.)ODBC Code (Cont.)
z Program sends SQL commands to the database by using SQLExecDirect z Result tuples are fetched using SQLFetch() z SQLBindCol() binds C language variables to attributes of the query result When a tuple is fetched, its attribute values are automatically stored in corresponding C variables. Arguments to SQLBindCol() Ö ODBC stmt variable, attribute position in query result Ö The type conversion from SQL to C. Ö The address of the variable. Ö For variable-length types like character arrays, The maximum length of the variable Location to store actual length when a tuple is fetched. Note: A negative value returned for the length field indicates null value z Good programming requires checking results of every function call for errors; we have omitted most checks for brevity.
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
ODBC Conformance LevelsODBC Conformance Levels
z Conformance levels specify subsets of the functionality defined by the standard. Core Level 1 requires support for metadata querying Level 2 requires ability to send and retrieve arrays of parameter values and more detailed catalog information. z SQL Call Level Interface (CLI) standard similar to ODBC interface, but with some minor differences.
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
JDBC JDBC
z JDBC is a Java API for communicating with database systems supporting SQL z JDBC supports a variety of features for querying and updating data, and for retrieving query results z JDBC also supports metadata retrieval, such as querying about relations present in the database and the names and types of relation attributes z Model for communicating with the database: Open a connection Create a “statement” object Execute queries using the Statement object to send queries and fetch results Exception mechanism to handle errors
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
JDBC CodeJDBC Code
public static void JDBCexample(String dbid, String userid, String passwd) { try { Class.forName ("oracle.jdbc.driver.OracleDriver"); Connection conn = DriverManager.getConnection( "jdbc:oracle:thin:@aura.bell- labs.com:2000:bankdb", userid, passwd); Statement stmt = conn.createStatement(); … Do Actual Work …. stmt.close(); conn.close(); } catch (SQLException sqle) { System.out.println("SQLException : " + sqle); } }
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
JDBC Code (Cont.) JDBC Code (Cont.)
z Update to database try { stmt.executeUpdate( "insert into account values ('A-9732', 'Perryridge', 1200)"); } catch (SQLException sqle) { System.out.println("Could not insert tuple. " + sqle); } z Execute query and fetch and print results ResultSet rset = stmt.executeQuery( "select branch_name, avg(balance) from account group by branch_name"); while (rset.next()) { System.out.println( rset.getString("branch_name") + " " + rset.getFloat(2)); }
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Functions and ProceduresFunctions and Procedures
z SQL:1999 supports functions and procedures Functions/procedures can be written in SQL itself, or in an external programming language Functions are particularly useful with specialized data types such as images and geometric objects Ö Example: functions to check if polygons overlap, or to compare images for similarity Some database systems support table-valued functions , which can return a relation as a result z SQL:1999 also supports a rich set of imperative constructs, including Loops, if-then-else, assignment z Many databases have proprietary procedural extensions to SQL that differ from SQL:
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
SQL Functions SQL Functions
z Define a function that, given the name of a customer, returns the count of the number of accounts owned by the customer. create function account_count ( customer_name varchar (20)) returns integer begin declare a_count integer; select count ( * ) into a_count from depositor where depositor.customer_name = customer_name return a_count; end z Find the name and address of each customer that has more than one account. select customer_name, customer_street, customer_city from customer where account_ count ( customer_name ) > 1
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Table Functions Table Functions
z SQL:2003 added functions that return a relation as a result z Example: Return all accounts owned by a given customer create function accounts_of ( customer_name char (20) returns table ( account_number char (10), branch_name char (15), balance numeric (12,2)) return table ( select account_number, branch_name, balance from account where exists ( select * from depositor where depositor.customer_name = accounts_of.customer_name and depositor.account_number = account.account_number ))
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Table Functions (cont’d)Table Functions (cont’d)
z Usage select * from table ( accounts_of (‘Smith’))
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Procedural Constructs (Cont.) Procedural Constructs (Cont.)
z For loop Permits iteration over all results of a query Example: find total of all balances at the Perryridge branch
declare n integer default 0; for r as select balance from account where branch_name = ‘Perryridge’ do set n = n + r. balance end for
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Procedural Constructs (cont.) Procedural Constructs (cont.)
z Conditional statements ( if-then-else ) E.g. To find sum of balances for each of three categories of accounts (with balance <1000, >=1000 and <5000, >= 5000) if r. balance < 1000 then set l = l + r. balance elseif r. balance < 5000 then set m = m + r. balance else set h = h + r. balance end if z SQL:1999 also supports a case statement similar to C case statement z Signaling of exception conditions, and declaring handlers for exceptions declare out_of_stock condition declare exit handler for out_of_stock begin … .. signal out-of-stock end The handler here is exit -- causes enclosing begin end to be exited
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
External Language Functions/ProceduresExternal Language Functions/Procedures
z SQL:1999 permits the use of functions and procedures written in other languages such as C or C++ z Declaring external language procedures and functions
create procedure account_count_proc( in customer_name varchar (20), out count integer ) language C external name ’ /usr/avi/bin/account_count_proc’
create function account_count( customer_name varchar (20)) returns integer language C external name ‘/usr/avi/bin/author_count’
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
External Language Routines (Cont.) External Language Routines (Cont.)
z Benefits of external language functions/procedures: more efficient for many operations, and more expressive power z Drawbacks Code to implement function may need to be loaded into database system and executed in the database system’s address space Ö risk of accidental corruption of database structures Ö security risk, allowing users access to unauthorized data There are alternatives, which give good security at the cost of potentially worse performance Direct execution in the database system’s space is used when efficiency is more important than security
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
The Power of Recursion The Power of Recursion
z Recursive views make it possible to write queries, such as transitive closure queries, that cannot be written without recursion or iteration. Intuition: Without recursion, a non-recursive non-iterative program can perform only a fixed number of joins of manager with itself Ö This can give only a fixed number of levels of managers Ö Given a program we can construct a database with a greater number of levels of managers on which the program will not work The next slide shows a manager relation and each step of the iterative process that constructs empl from its recursive definition. The final result is called the fixed point of the recursive view definition. z Recursive views are required to be monotonic. That is, if we add tuples to manger the view contains all of the tuples it contained before, plus possibly more
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Example of Fixed-Point ComputationExample of Fixed-Point Computation
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Advanced SQL FeaturesAdvanced SQL Features
z Create a table with the same schema as an existing table: create table temp_account like account z SQL:2003 allows subqueries to occur anywhere a value is required provided the subquery returns only one value. This applies to updates as well z SQL:2003 allows subqueries in the from clause to access attributes of other relations in the from clause using the lateral construct: select customer_name, num_accounts from customer , lateral ( select count (*) from account where account.customer_name = customer.customer_name ) as this_customer ( num_accounts )
Computing & Information Sciences CIS 560: Database System Concepts Mon, 11 Sep 2006 Kansas State University
Advanced SQL Features (cont’d)Advanced SQL Features (cont’d)
z Merge construct allows batch processing of updates. z Example: relation funds_received ( account_number, amount ) has batch of deposits to be added to the proper account in the account relation merge into account as A using ( select * from funds_received as F ) on (A .account_number = F.account_number ) when matched then update set balance = balance + F.amount
